Blender API: Return value of bpy.data.objects(ID).show_bounds and .bound_box
Object.bound_box does not contain mathutils-types like Matrix or Vector, it's a plain property array of float[3] which has no representation format like other types do.

You need to iterate over all elements and print them, e.g.:

for b in bpy.context.object.bound_box:
    print(b[:])

# (-1.0, -1.0, -1.0)
# (-1.0, -1.0, 1.0)
# (-1.0, 1.0, 1.0)
# (-1.0, 1.0, -1.0)
# (1.0, -1.0, -1.0)
# (1.0, -1.0, 1.0)
# (1.0, 1.0, 1.0)
# (1.0, 1.0, -1.0)


Or make a list of Vector objects:

[Vector(b) for b in bpy.context.object.bound_box]